[time-nuts] Discipline an oscillator with NTP?

Bob Camp lists at rtty.us
Sat Jul 23 17:01:06 UTC 2011


Hi

There is a range in what NTP will do, just as there is a range in what you can do via zero beat to WWV. You can get to a ppm or so via zero beat most of the time. Under good conditions you can get to 0.1 ppm. A practial NTP system running to servers over the net has roughly the same accuracy. Time constant of 10,000 seconds, time accuracy / stability of 1 to 10 ms. 

Bob

On Jul 23, 2011, at 12:49 PM, paul swed wrote:

> Yes but zero beat by ear is terrible. Are you talking a scope and I think
> thats only 1 X 10-7 as I recall.
> Regards
> Paul.
> 
> On Sat, Jul 23, 2011 at 12:42 PM, Bob Camp <lists at rtty.us> wrote:
> 
>> Hi
>> 
>> The simple answer is that normal NTP via the net will give you accuracy
>> similar to the "zero beat to WWV" approach. It will take a few days to get
>> to that level. Much faster to fire up the radio and use WWV.
>> 
>> Bob
>> 
>> On Jul 23, 2011, at 12:29 PM, paul swed wrote:
>> 
>>> I may be reading way to much into the question.
>>> But the goal discipline the local oscillator as an alternate to GPS or
>> WWVB
>>> etc
>>> Further assumption get the same types of services out of the oscillator
>>> Frequency and time plus pulses.
>>> 
>>> That said if its one ntp source you look at, potentially far down stream
>>> with many network hops, doesn't that make your reference only as good as
>>> that ntp server as it jitters around?
>>> 
>>> Would it be better to track say 3 servers hopefully up toward the top of
>> the
>>> ntp service. Analyze their behavior to each other to attempt to account
>> for
>>> network behaviors and the server behaviors.
>>> 
>>> Essentially compare all three and derive a number to adjust the local
>>> oscillator.
>>> 
>>> I might add that by adding any 1 pps source from radio or GPS while
>>> available would really let you understand what jitter and path delays you
>>> are getting and then establish the adjustment. (Fully understand that the
>>> path is variable in IP.
>>> 
>>> Love simple but I suspect, its much tougher then that otherwise why mess
>>> with GPS at all.
>>> ;-) Its that darn radio stuff.
>>> Regards
>>> Paul
>>> WB8TSL
>>> 
>>> 
>>> On Fri, Jul 22, 2011 at 10:25 PM, Chris Albertson <
>> albertson.chris at gmail.com
>>>> wrote:
>>> 
>>>> Yes but in this case it really is easy;  Below is an outline (don't
>>>> try to compile it.).  It has a slight problem because just using
>>>> "sleep" is kind of simplistic.  One should wait on the new second and
>>>> add some error chacking   Point here is just to show  that this is not
>>>> weeks and weeks worth of work".  The below pulse a bit every second
>>>> and if the system is running NTP then the length of a second is
>>>> controlled by NTP.
>>>> 
>>>> Main()
>>>> {
>>>> int status;
>>>> int fd;
>>>> int pw = 1000  /* pulse width in uS */
>>>> fd=open("dev/tty",O_RDWR);
>>>> while(1) {
>>>> status = 1;
>>>> ioctl(fd, TIOCMSET, &status);
>>>> ussleep(pw);
>>>> status = 0;
>>>> ioctl(fd, TIOCMSET, &status);
>>>> ussleep(1000000-pw);
>>>> }
>>>> }
>>>> 
>>>> On Fri, Jul 22, 2011 at 6:08 PM, Jim Lux <jimlux at earthlink.net> wrote:
>>>>> On 7/22/11 3:46 PM, brent evers wrote:
>>>>>> 
>>>>>> "After that all you need to do is write some code to..."
>>>>>> 
>>>>>> Oh - if I had a nickel for every time I've heard that!
>>>>>> 
>>>>>> Brent
>>>>>> 
>>>>> 
>>>>> When I worked in the physical effects business, we'd get a set of
>>>>> storyboards from a director, and we'd have to figure out how we were
>>>> going
>>>>> to build a rig or arrange the effect as required.   The catch phrase
>> was
>>>>> always "then, all you gotta do is"...
>>>>> 
>>>>> representing some sort of incredibly difficult, tedious, or impractical
>>>>> activity. Sure, install 10,000 lightbulb sockets into a frame and wire
>>>> them
>>>>> up before tomorrow morning's call time at 6AM.. *all you gotta do* is
>> get
>>>> 50
>>>>> people to each wire 200 sockets, screw in the bulbs and test them.
>>>>> 
>>>>> _______________________________________________
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>>>>> and follow the instructions there.
>>>>> 
>>>> 
>>>> 
>>>> 
>>>> --
>>>> 
>>>> Chris Albertson
>>>> Redondo Beach, California
>>>> 
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